1. Field of the Invention
This invention relates to a device for calculating the quantity of light and, particularly, to a device for calculating the quantity of light used when an ultraviolet light-curable tape stuck to one surface of a wafer is irradiated with ultraviolet light.
2. Description of the Related Art
In the field of semiconductor production, the sizes of wafers are increasing year after year and, besides, the thickness of the wafers is decreasing to increase the mounting density. To conduct the back-grinding which is for grinding the back surface of the semiconductor wafer for decreasing the thickness of the wafer, a surface protection tape is stuck to the front surface of the wafer for protecting the semiconductor elements formed on the front surface of the wafer. The surface protection tape is peeled off after the back-grinding. If the surface protection tape has a relatively large adhering force at the time of peeling, however, it is probable that the wafer itself is damaged being pulled by the surface protection tape and, besides, the adhesive of the surface protection tape partly remains on the surface of the wafer. In recent years, therefore, there has been used, as a surface protection tape, a tape (hereinafter referred to as “ultraviolet light-curable tape”) of which the adhesive is cured by the irradiation with ultraviolet light (hereinafter often referred to as “UV”) to exhibit a decreased adhering force. During the back-grinding, the surface protection tape exhibits a sufficiently large adhering force as it has not been irradiated with ultraviolet light. After the back-grinding, however, the adhering force is lowered by the irradiation with ultraviolet light. This makes it possible to easily peel the surface protection tape off the wafer without damaging the wafer and without leaving the adhesive thereon.
The wafer having semiconductor elements formed on the surface thereof is finally cut into dices by dicing. At the time of dicing, the wafer is integrated with a frame by using a dicing tape stuck to the back surface of the wafer. Then, the wafer is cut together with the dicing tape (in the case of a full cut) by using a dicing blade of a dicing device. However, a problem in that the adhesive of the dicing tape sticks to the blade causing the clogging and damaging the semiconductor elements occurs. Therefore, it has been attempted to avoid the above problem by using an ultraviolet light-curable tape as the dicing tape, and lowering the adhering force by curing the dicing tape, to some extent, by irradiation with the ultraviolet light prior to dicing. In this case, irradiation with an excess of ultraviolet light results in a great reduction in the adhering force which may permit the die to be scattered at the time of dicing. Therefore, the dicing tape is irradiated with ultraviolet light of which the quantity is limited to some extent (see, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 10-27836, 10-284564 and 7-183365).
However, the ultraviolet light-curable tape exhibits adhering force that varies depending upon the kind of the tape, and it is difficult to determine a proper quantity of ultraviolet light. In particular, the adhering force of the ultraviolet light-curable tape may vary depending upon the production lot and the elapsed time. In such a case, the quantity of ultraviolet light is determined relying solely upon the operator's experience and can seriously affecting the yield.
That is, when the quantity of light is insufficient while using, for example, the ultraviolet light-curable tape as the surface protection tape, the above-mentioned problem of breakage of the wafer and the residence of the adhesive occurs. When the quantity of light is insufficient while using, for example, the ultraviolet light-curable tape as the dicing tape, there occurs the problem in that the adhesive of the dicing tape sticks to the blade as described above. Further, when the quantity of light is excessive, while using, for example, the ultraviolet light-curable tape as the dicing tape, the adhering force drops and a die scatters at the time of dicing.
The present invention was accomplished in view of the above circumstances and has an object of providing a device for calculating the quantity of light to automatically calculate the quantity of light needed for the ultraviolet light-curable tape while avoiding the problems caused by an insufficient quantity of light or an excess quantity of light.